The present invention relates to a data storage and retrieval system for retrieving data distributed and stored on a network and presenting the retrieved data by a user-desired presentation form.
This application is based on Japanese Patent Application No. 9-289770, filed Oct. 22, 1997 and Japanese Patent Application No. 9-307460, filed Nov. 10, 1997, the contents of which are incorporated herein by reference.
Generally, data is based on a personal intention and interpretation. Because of the personal preference, data to be provided is constructed from the viewpoint based on the data provider. The provider constructs data to maximize the utility function of the provider and provides the data. A user to which the data is provided also has a utility function and a demand for referring to and processing the data to maximize the utility function of the user.
The architecture of a recent database system is modeled as a three-layer schema. An external schema layer is closest to the application layer of the three-layer schema. This layer provides a specific method (view or presentation form) of viewing a data structure as part of a database to a specific user (or group). Such a database system places prominence to prevent a physical or logical change in the data structure from influencing on the application software rather than to reconstruct the retrieved data in accordance with the viewpoint of the user.
In the conventional framework of database, an end user is not allowed to freely manipulate the view for the database, and no mechanism is available to allow a plurality of users to share view for the database. That is, only viewing based on the database developer/manager is present. The view is associated with not data expression or data behavior but the data structure. As described above, with the conventional view for the database, the data can hardly be reconstructed in accordance with the viewpoint of the user in the true sense.